Draw die



United States Patent 3,382,690 DRAW DIE Howard S. Achler and HamidKaufmann, Chicago, 111

assignors to Kaufmann Tool & Engineering Corp., Clucago, 111., acorporation of Illinois Filed Sept. 17, 1965, Ser. No. 488,048 4 Claims.(Cl. 72-57) ABSTRACT OF THE DISCLOSURE An improved mechanism for drawingsheet steel and the like is provided by use of a female die defining theshape to which the sheet is to be drawn, and a retainer for cooperationwith the female die, wherein the retainer uses a rigid insert spacedfrom the walls of the retainer to define a well, and at least two diepads of urethane rubber are used in the retainer with at least theuppermost pad overlying the rigid insert and arranged to enter therecess of the female die and at least the lowermost pad providingportions that flow in the well during a drawing operation. A preferredsize of urethane rubber pad is disclosed to have a thickness in therange of /2 to 1 inch. In one form of device one of the pads is providedin annular shape for entry into said well.

This invention relates to a drawing mechanism and more particularlyrelates to a drawing mechanism that utilizes, as a working portionthereof, a flexible solid element that performs, when deflected, in muchthe manner of a liquid by providing substantially uniform pressuretherefrom in all directions. I

The process of drawing sheet material is well known and, for purposes ofprecision herein, must be carefully distinguished from the process ofembossing. Die Design Handbook, McGraw-Hill Book Company, SecondEdition, 1965, at pp. -1 states: Drawing is a process of cold forming aflat precut metal blank into a hollow vessel without excessivewrinkling, thinning or fracturing. In embossing, the material of theblank surrounding the bead portion being embossed or distorted is griped or held by relative large pressures, or because of the proportion ofthe bead to the blank being very small, so that as a result the materialof the blank generally resists movement and the small portion of theblank being acted upon actually stretches, thus causing relative severethinning of the portion of the material being embossed. In drawing, theportions of the material being acted upon are desired to deform to theultimate shape without undue thinning down of the material.Consequently, the material surrounding the portion thereof beingdeformed is not to be held by relatively large pressures, and the diesare normally designed to permit the material being drawn to fiow to thedesired condition and position. Hence the reduction in overall area sizeof the blank dimension is very much greater in drawing work.

Now, in drawing mechanisms for producing cupped or hollow-vesselproducts, it is normal practice to provide cooperating and carefullymatched male and female dies to achieve the desired deformation. Theamount of draw necessary to achieve the desired end product may dictatedrawing of the blank of material in a series of progressive steps whichrequires the provision of multiple matched sets of dies. Such tooling isexpensive, and, unless used in very high production runs, addsmaterially to the per unit cost of production of the end product.

Thus, one object of this invention is to provide a drawing mechanismwhich avoids the necessity of a carefully matched die set and which ischaracterized by its simplicity and inexpensiveness of construction.

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Another object of this invention is to provide a drawing mechanism whichrequires in a drawing die only a female die to define the exterior ofthe shape desired and the provision of multiple pads of urethane rubberfor cooperation with the female die.

Further objects and advantages of this invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize this invention will be pointed out with particularity inthe claims annexed to and forming part of this specificatlon.

A preferred embodiment of the invention is shown in the accompanyingdrawings, in which:

FIG. 1 is a vertical cross-sectional view through the diemechanism ofthis invention showing the arrangement of parts prior to the deformationof the blank;

FIG. 2 is a view similar to FIG. 1 but showing the arrangement of partsat the end of the deformation process;

FIG. 3 is a top plan view of the retainer or lower portion of the diemechanism shown in FIG. 1;

FIG. 4 is a vertical cross-sectional view similar to FIG. 1 but showinga modified form of draw die; and

FIG. 5 is another view, similar to that in FIG. 2 of the modified formof draw die of FIG. 4.

Referring now to the drawings, there is shown in FIG. 1 a female die 10formed of steel and which defines side walls and the bottom for an openfemale-die recess 12 that is shaped to provide the outer contour of thehollow vessel that is to be formed from a plat precut metal blank thatis to be drawn. The female die is mounted, as shown, on an appropriatebase, or backing plate 14.

The other portion of the drawing mechanism is a retainer means, and itincludes a base, or backing plate 16 having mounted thereon an uprighthollow retainer 17 that provides a peripheral wall means 18 surroundinga cavity 20 into which a portion of the die 10 enters during the drawingprocess. In the bottom of the cavity 20, mounted on the backing plate16. is a rigid steel insert 22 that is shaped to be generally protrudingor convex and is spaced centrally in the cavity 20 so as to define awell 24 between the insert 22 and the spaced retainer walls 18.

Also positioned in the retainer cavity 20 are a plurality of die pads 26of urethane rubber. The plurality of die pads 26 of urethane rubber arelaid one upon each other as shown in FIGS. 1 and 2, with a lowermost pad260 overlying the rigid insert 22 and being of an areal dimension thatis at least as large as the areal size of the cavity 20, so that theedges of pad 26a engage the walls 18 of the retainer. At least oneadditional pad 26b is provided positioned in cavity 20. Preferably thepads 26]) are of the same areal size as the lowermost pad 26a, as shownin FIG. 1, but it will be understood that such is not required. In FIG.1 a precut blank of metal that is to be shaped to define a hollow vesselis shown at 28 and is positioned on the upper surface of the uppermostdie 26b. The areal size of the cavity 20 is selected to be at leastslightly greater than the size of the blank 28. The female die 10 ispreferably provided with at least one air vent 30 communicating with thedie recess 12 adjacent the innermost portion thereof.

While the steel insert 22 shown appears in the form of a plate withrounded edges, it will be understood that the shape and height of theinsert may be varied as desired to provide a very general approximationto the shape of the recess in the female die and forming a well 24,between it and the retainer walls 18, into which a portion of theurethane rubber may flow, as seen in FIG. 2, during a drawing operation.The thickness of the urethane pads 26 should be in the range of inch to2 inches, and preferably is in the range of substantially /2 to 1 inch.Although the insert 22 is preferably of steel, it will be appreciatedthat it can be made of other hard materials, such as other metals orwood, and may even be made of urethane of a greater durometer reading,or hardness index, as compared with that of at least Shore A. Excellentresults have been obtained using pads having a hardness index -90 ShoreA, and using an insert 22 of Shore A or harder.

In use, in the form of device of FIGS. 1-3, at least two urethane pads26a and 2612 are selected for overlying each other and the steel insert22, and a precut blank of material 28 is positioned on the uppermost pad26b centrally relatively to the recess 12 in the female die 11). Uponbringing the drawing mechanism together in the manner shown in FIG. 2the female die 10 operates against the pads of urethane rubber to effecta drawing of the blank to the finished condition of the hollow vessel asshown in FIG. 2.

The applying of pressure to the urethane rubber pads 26 causes theurethane rubber to fiow into the recess 12 and to exert substantiallyuniform pressure in all directions against the blank 28 causing same todeform to assume the contour of the female-die recess 12 and therebyforming the part by drawing. Sufiicient numbers of pads 26 are used tocause the blank 28 to be formed in a single pass. If wrinkling occurs inthe finished product, one may assume that insuflicient pressure is beingdeveloped and that an additional pad 26 of urethane rubber should beadded in the retainer cavity 20. If tearing, or fracture, or thinning ofthe blank occurs, one may assume too many die pads are being used, andthe number reduced accordingly, but at least two die pads are to be usedin the drawing process of this invention, as only a single die pad doesnot provide for the necessary relative movement between the die pads 26to achieve an acceptable draw. Because of the uniform and high pressuresdeveloped in the urethane rubber by the die 10 moving against the pads26 and the rapidity with which the drawing is accomplished, it isdesirable to vent the female recess 14, and at least one vent means 30is provided in the die 10 communicating with the recess 12. The ventmeans 30 also permits of release of the shaped vessel 32 from the cavity14. The use of multiple pads 26 of the same areal shape permits ofinterchange thereof whenever the outermost pads begin to wear or abrade.Because of the tendency to express air from the retainer 17 during adrawing operation, if necessary a bent bore 32 may be provided centrallyin each pad 26, and at least in the uppermost pad 26b. In the form ofdevice of FIGS. 4 and 5 elements corresponding generally with earlierdescribed elements are given the same reference numeral in the series.Thus, the female die provides an open female-die recess 112 that isvented by a plurality of vent passageway means 130. The retainer meansincludes a base 116 having an upright hollow retainer 117 that providesperipheral wall means 118 surrounding a cavity 120 in which ispositioned an insert 122 spaced from walls 118 to define a well or airspace 124 therebetween.

Positioned in cavity 120 is a lowermost urethane rubber die pad 126athat is annular in shape to enter and be positioned in well 124 and anuppermost urethane rubber die pad 126b which is sheet-like in appearanceand has an areal dimension that is substantially the same as the arealdimension of cavity 120. The precut metal blank is at 128 positioned onpad 12617. An air vent 132 is preferably provided centrally in pad126]). Additional pads corresponding in size and shape with pad 126])may be provided as necessary. The pad 126a operates to provide forgreater blank-holding pressure in the annular region surrounding insert122 and during the blank-drawing operation. in use, the pads 126a and126b deform substantially to the shape shown in FlG. 5, the size of thewell 124 being selected to accommodate the bulging of pin! 126a.

While the shape of the die recess 12 is shown as a simple geometricalshape or as the surface of a body of revolution, it will be understoodthat more complex die recesses may be provided depending upon the shapeto be produced. Again, while the peripheral shape of cavity 20 is shownsquare in FIG. 3, it will be understood that the cavity 20 may also havea circular or rectangular periphery or other shape as desired.

The passageways 130 in female die 110 may also be provided withcompressed air therethrough after a drawing operation, in order to ejectthe formed part from the die. While the die is described herein for usewith precut blanks, it will also be understood that the mating dies 10and 18 of FIGS. 13, or 110 and 118 of FIGS. 4 and 5 may be used toproduce a shear action which converts the dies to one which perform botha blanking action from a sheet of material and a drawing function.

While there has been shown and described a particular embodiment of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made therein without departing from theinvention, and therefore, it is intended in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What we claim as new, and desire to secure by Letters Patent of theUnited States is:

1. A drawing mechanism for steel and the like comprising, incombination: die wall means defining sidewalls and the bottom of an openfemale die recess; retainer means including a base, peripheral wallmeans on the base and cooperating with the base to define a cavity intowhich a portion of the die wall means of the female die may enter duringthe drawing process; a rigid insert in the cavity of the retainer means,the insert being spaced from said wall means to define a well betweenthe insert and the walls of the retainer; and at least two separate diepads of urethane rubber lying one on top of the other in said cavity,and with at least the uppermost one of said die pads overlying the rigidinsert and arranged to have portions thereof enter the recess of thefemale die and with at least the lowermost one of the die pads providingportions thereof positioned to flow in said well during a drawingoperation.

2. A drawing mechanism for sheet steel and the like comprising, incombination: a female die with a forming recess therein, a retainerdefining a walled cavity of greater area dimension than the size of theblank to be drawn; a rigid insert in said cavity extending in thedirection toward the recess in the female die; a plurality of die padsof urethane rubber in said cavity with at least one of said pads laidupon another pad and over the rigid insert; and the insert being spacedcentrally of the cavity to define a well between the insert and thewalls of the retainer into which portions of the urethane rubber mayflow during a drawing operation.

3. A device as set forth in claim 2 wherein one of said pads of urethanerubber has an annular shape for entry into said well, and another ofsaid pads of urethane rubber overlying said one pad and said insert.

4. A device as set forth in claim 2 wherein at least one of the pads ofurethane rubber is of areal dimensions approximating at least the arealsize of the walled cavity and is of a thickness in the range ofsubstantially /2 inch to 1 inch.

References Cited UNITED STATES PATENTS 840,921 l/1907 Dickey 726O1,267,591 5/1918 Rehbein 7257 2,239,339 4/1941 Oeckl 72-60 2,280,3594/1942 Trudell 726O 3,121,944 2/1964 Karau 72-57 FOREIGN PATENTS 584,3659/1933 Germany.

RICHARD J. HERBST, Primary Examiner.

